"Just ask Carol" is a flawed agony aunt column that the Grauniad runs, applying the lessons of evolutionary psychology to specific problems. That is the byline, but her first question derived most of its answer from studies of other species. Call me a spoilsport but, to me, family life is more complex than a simple comparison with chimpanzees reveals.
The human element is supplied by a shared hobby. And as to the suggestion that...
You could encourage big brother to be involved in the grooming of little brother, perhaps with hair washing and skin moisturising, and in time the youngest should reciprocate.
That may prove a singular failure given the number of cultural norms that it could transgress. Sentences least likely to manifest bonding include: “Let us moisturise together” or “May I groom you?”.
Has Carol started any fights yet?